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  1. #1
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    PV panel oriantation vs horizon shading in winter

    Like 99% of installations I see around here my panels are mounted on the roof in portrait (longest side vertical). Now in the UK winter is upon us and the sun is low in the sky, fortunately my roof is quite steep (52deg) so I still get a reasonable output however being a bungalow with a low roof some items on the horizon now shade the panels when they do not in summer. The horizon shading starts at the bottom of the panels and creeps up as the sun sinks in late afternoon.

    The panels are 10 rows and 6 columns with shading diodes connected across each pair of columns however the shading occurs across all columns at once hence the diodes do nothing and the string output current is reduced to that of the shaded cells alone.

    I now realize that if the panels were orientated in landscape (longest side horizontal) the shading diodes would work as intended as the horizon shading would blank out entire rows at once forcing the shading diodes to conduct across unproductive rows maintaining the strings output current to that of the unshaded cells.

    Am I missing something here or are most installations not good with horizontal horizon shading ?

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  2. #2
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    Re: PV panel oriantation vs horizon shading in winter

    It doesn't matter whether the panel is vertical or horizontal. I guess your talking about the same panels from your previous thread. I'm not and expert but I agree that you would be better off laying the long side horizontal. If you have to move the mounting hardware you may as well put it higher on your roof. From the photos it looks like there down near the overhang.



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  3. #3
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    Re: PV panel oriantation vs horizon shading in winter

    Quote Originally Posted by Kajunbee View Post
    It doesn't matter whether the panel is vertical or horizontal.
    Ahh but I think it does matter and that's what I am very badly trying to explain, the panel is 10 cells x 6 cells. Each string of 10 cells is connected in series and then adjacent strings of 10 cells are connected in series with a shading diode across the other end so there are 3 shading diodes in total each handling 20 cells.

    Now imagine as is currently the case the shading occurs evenly across each set of 20 cells then the shading diodes do nothing and the panel output current cannot rise above that of the shaded cells. However if one group of 20 cells is shaded whilst the other two groups of 20 are not then the shading diode will conduct across the shaded group allowing the output current of the panel to equal the unshaded cells.

    So for the situation that I have where the shading is a horizontal band climbing up the array landscape panel orientation would definitely give higher output.

    However I have to agree shifting the whole lot higher up the roof would be very effective except I am not as agile as I was and it would make cleaning them with a sponge on the end of a garden cane as I presently do impossible. I am in a windy farming area and some soil gets deposited on them in the summer.

    I have a near neighbor with a similar sized roof with two rows of 8 panels in portrait (~4Kw+) and I see the lower row often in part horizontal shade and I wonder if the system performance would have been better if they were in landscape, but potentially the downside is more fixing hardware (rails, mounts etc) and that may be why I see them always portrait. As for me I simply copied everybody else without thinking about it :)

    BTW this site is annoying timing you out when you take a while to write a reply!



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    Re: PV panel oriantation vs horizon shading in winter

    It might help if you reflect sunlight onto the shaded area. Shiny sheet metal, strips of aluminum tape, etc. Mount it at the uproof edge of the PV panel. Give it flexibility in case of strong winds.

    this site is annoying timing you out when you take a while to write a reply!
    When you log on, try checkmarking the 'Remember Me' box. If I neglect this then the system kicks me off after a few minutes.


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    Re: PV panel oriantation vs horizon shading in winter

    Yes , I think there are some gains to be had by placing panels horizontal.What i wonder about is that the shade will then effect a larger portion of the panels. Suppose you have even shading across the panels end to end.The way your panels are now when the bottom row of cells are shaded it effects 24 individual cells. If you turn the cell horizontal and the lower edge is the same heighth as the vertical placed panel then 40 cells will be shaded. Now you have the situation of either 24 cells shaded without the function of the bypass diode. Or 40 cells shaded with the function of the diodes. Now turning the panels horizontal and keeping them at the upper height you can comfortably reach would be best.

    I think you could do and experiment if you feel like it's worth the trouble. On one panel shade one column of 10 and note the difference in output. Then block one row of 6 cells across the bottom and note the difference in output. If your clever enough you might be able to do the experiment without climbing on the roof. And someone to assist you so you don't have to go back and forth to the monitor.



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  6. #6
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    Re: PV panel oriantation vs horizon shading in winter

    Hello and thank you :) I am clean out of decent sun right now BUT I did finally do a simulation run of no shade vs 1 row or 1 column and here are the results (sorry about the picture quality) for a single 260W panel using a shading factor of *0.25.

    When the shading diode is activated (10 cells shaded) the output has the classic twin hump mpp (140 & 70W) and I am certain my simple P&O controller would stay with the false one if the shadow appeared during normal operation and even during a cold start as it begins with no load on the panels so highest voltage first.

    So without changing my mppt software to include a scan phase or some other method of avoiding the false mpp re-orientating the panels although theoretically giving a higher output would not help me anyway :(
    Click image for larger version. 

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